Pin mills are used to grind various types of bulk goods. The material to be ground is thereby most often introduced near the axis into a grinding space between two coaxially arranged grinding discs. The grinding discs have grinding pins alternately arranged in concentric circles. The material introduced for grinding is transported outward due to the rotation of the grinding disc and is shredded by the grinding pins of the two grinding discs moving past each other until the desired particle size is reached. Due to the use of two instead of one driven grinding disc in counter-rotating pin mills, the relative speed of the pins moving in opposite directions doubles, whereby a better grinding is achieved. Counter-rotating pin mills are often used to grind food products. Strict legal regulations (regarding hygiene) exist for the processing of food products. For example, it is necessary to clean the grinding space of pin mills regularly and most often manually without using means harmful to health. It is thereby not possible to open the grinding housing using a simple pivot mechanism where one grinding disc is attached to one housing part due to the large diameter of the interengaging grinding discs and the grinding pins rotating close to each other. The grinding pins would contact each other and would be bent.
WO 93/04780 A1 describes an installation for grinding grain which comprises a pin mill with two grinding discs driven in a counter-rotating manner. An opening of the housing for cleaning purposes is not described.
DE 28 28 029 A1 describes an installation for grinding hop which also comprises a counter-rotating pin mill. This pin mill has a one-sided axial material supply as well as a housing divided into two parts in the grinding plane vertically to the grinding axis. The exact opening mechanism is not described.
U.S. Pat. No. 4,378,911 A describes a cage mill for grinding ore which is of a two-part design and has a rail structure arranged in the base as well as a drive unit that allows the two housing halves to be moved apart.
WO 2013/085476 A1 describes a grinding device with two coaxially arranged hollow grinding shafts by which organic bulk material is supplied to the grinding space, wherein the inner ends of the grinding shafts are provided with mutually parallel grinding discs having grinding members arranged on concentric circular paths. It is very difficult, especially with counter-rotating pin mills having a two-side axial supply, to access the grinding space for cleaning or maintenance without having to perform (both before and thereafter) extensive dismantling and assembly work. The grinding material supply devices and the drives must be separated from the housing parts in an intricate manner. The prior art does not disclose any satisfactory solution.